Fluctuating voltage meter

Problem in alternator/generator, requires technician.

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

Get a volt meter, start your car and see how many volts your car is producing while running. Should be around 14 volts. May want to watch the meter for a while since your electric seems to fluctuate. Most voltage regulators are internal of your alternator. If you are getting a lot more or less than 14 volts while running, replace the alternator. If it is not charging, voltage will drop as vehicle runs, until battery is dead.

Hello,
When you say battery voltage how are you testing it? Are you looking at a gauge on the dash? Or are you physically testing it with a multi meter? If the truck is dying and you recently replaced the alternator and battery I would first suggest you to check all them connections again real good. Snug them all up. Check for corrosion and clean as needed. Did you replace the battery and alternator with new/re-manufactured battery and alternator? The alternator needs to put out at least 13.6 volts to charge your 12 volt battery or the battery will not maintain a charge. However the alternator runs the vehicle once it is started. The battery is used only to start the car and then the alternator runs it. So if your vehicle starts and runs and then dies you may have a bad alternator. Check your connections first and then test the alternator with a multi meter. Anything less than 13.6 volt will not suffice. 14+ volts would be the hopeful output of a good alternator.
regards, Tony

it sounds like you have a parasitic draw when the truck is shut down. Your test does not test any thing. You need to put an ammeter between a battery post and its cable. You need to measure in miliamps (one thousandth of an amp). Draw should be about 50 miliamps.
A simple test is to just disconnect the battery at night for a few days and see if that solves the problem. If yes, you are chasinig something that is drawing current (amps) while the trcuk is off. Yoiu also should check to see if the battery voltage is around 14 volts with the engine running, that would tell you the alternator is working and charging the battery.

Make, model & Year?

This could be the alternator. Bring your vehicle to a shop and have them test both the battery and the alternator. I have seen brand new batteries come off the shelf and fail so it could be either

A 76, huh, let's see, I don't know if that had the regulator in there or not. It sounds like the alt died, but maybe not. It won't run without the alt. And will only last about 20 mins on a full battery. I would take the alt off and get it back to the store to have it checked. That would be the quickest way to tell, just because it is new doesn't mean it is good. Don't keep on killing the battery, it can only handle so many drains. Hope this helps.

Hi,

There are two main possibilities here.

1) The battery is flat because it is no longer holding a charge. The ability of a battery to retain a charge will diminish over time. In this case a replacement battery is needed.

2) There is a problem with the alternator which is not supplying charge to the battery when the vehicle is running causing the battery to be drained over a period of time.

You can test for both of these using a multimeter and this is very easy to do.

1) With the meter set to the DC scale and attached to the terminals of the battery (Red lead to Positive, Black to Negative) and with all accesories turned off - you should have a reading above 9.6 volts. If the reading is less than this the battery is faulty and needs to be replaced.

2) If the reading is above 9.6 volts, you need to get the car running in order to test your alternator. You will need someone to rev the engine whilst you connect the meter to the battery. With the engine at a fast idle, and all accessories off, the voltage on the meter should read around 14 volts (13.5 to 14.4) showing that the alternator is producing a reliable charge.

Anything less than 12 volts with the engine running means the alternator is at fault and it is the alternator that needs to be replaced not the battery.

You can also test with accessories on (heater, lights etc,,) The reading should still remain around 14 volts with these extra drains on and the engine at fast idle. Anything less is an indicator of a faulty alternator being the cause of your problem.

Hope this helps. Thanks for using FixYa.

They have expensive tools and equipment to test alternators but you can get by with a simple digital volt meter. With the volt meter on DC voltage attach each lead to the corresponding terminals on the battery. With the engine running and all the electrical loads on (such as the head lights, radio, defrost, wipers, radio etc). the voltage reading should be between 13 and 14 volts. If you actually only have 9 volts then the alternator isn't charging and you'll have to look in to that more. The truck wouldn't be able to start or run very well with only 9 volts so i'd be willing to bet the gauge is bad or possibly a wiring fault.

Have you checked the charging of the alternator at the battery? (not by a parts store) Put a volt meter across the battery and check voltage while running. You should be showing 13.5v or better (not over 14) with accessories off, 12.5 or better with everything on including high beams. If you don't, chances are you may have a regulator problem. I don't know how you are checking draw, but you should be using an ammeter placed between either battery terminal and cable (cable removed from battery) Unplug each fuse and watch for a substantial drop in draw. That system will be the one with the problem...then, unplug each component served by that fuse (with fuse replaced) till the draw again drops. That will be the component that is pulling your battery down. You did check the simple stuff like sun visor lights and glove box light?

Are you leaving something plugged into the Cigarette lighter by chance as that will drain it even if nothing's charging.

You may have a faulty ground somewhere, but that will be really hard to trace as you would have to test each wire...